I85PREP
⌘ K
BTEB Diploma in Marine Engineering Examination study materials
BTEB Diploma in Marine Engineering Examination study resources

BTEB Diploma in Marine Engineering Examination practice questions

One question at a time. Build your BTEB Diploma in Marine Engineering Examination understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Marine Propulsion Systems and Main Engines

In a four-stroke marine diesel engine, which valve is normally fitted with a rotator to distribute wear and prevent carbon build-up on the seat?

  1. The fuel injection valve
  2. The air starting valve
  3. The cylinder relief valve
  4. The exhaust valve Correct answer.

Explanation

Exhaust valves operate at very high temperature and are prone to seat pitting and carbon deposition. A valve rotator turns the valve slightly on each opening so that the seating face and stem wear evenly and deposits are wiped off. Fuel, starting and relief valves do not need this treatment.

Question 2Marine Propulsion Systems and Main Engines

What is the primary function of the scavenge air receiver in a large two-stroke crosshead engine?

  1. To separate water from the lubricating oil
  2. To cool the exhaust gas before the turbocharger
  3. To supply a steady charge of pressurised air to the cylinder under the scavenge ports Correct answer.
  4. To store compressed air for starting the engine

Explanation

The scavenge air receiver acts as a reservoir between the turbocharger/air cooler and the cylinder liner ports. It smooths pressure pulsations and delivers an even flow of charge air for scavenging and combustion. Starting air is held in separate starting air receivers.

Question 3Marine Propulsion Systems and Main Engines

Which component transmits the gas load from the piston to the connecting rod in a slow-speed two-stroke engine?

  1. The crosshead Correct answer.
  2. The thrust block
  3. The telescopic pipe
  4. The piston skirt

Explanation

In a crosshead engine the piston rod is bolted to a crosshead that slides in vertical guides. The crosshead absorbs the transverse reaction from the inclined connecting rod and passes the gas force to the connecting rod and crankshaft. The piston skirt therefore carries no side thrust.

Question 4Marine Propulsion Systems and Main Engines

The purpose of the fuel pump lead (spill timing) in a jerk-type fuel injection pump is to determine which parameter?

  1. The quantity of fuel delivered per stroke
  2. The atomisation quality of the injector nozzle
  3. The moment of injection relative to top dead centre Correct answer.
  4. The temperature of the fuel at the pump inlet

Explanation

The lead or spill timing fixes the point in the cycle at which the pump plunger closes the spill port and begins to pressurise the fuel. This sets the start of injection relative to TDC, which governs combustion timing. Quantity is set by the plunger helix position, not by the lead.

Question 5Marine Propulsion Systems and Main Engines

Why is a cooling water space provided around the exhaust valve seat in a diesel engine cylinder head?

  1. To reduce the clearance volume
  2. To increase the compression ratio
  3. To keep the valve seat material below its safe working temperature Correct answer.
  4. To preheat the fuel before injection

Explanation

Exhaust valve seats are exposed to hot combustion gas and must be cooled to avoid softening, cracking and seat distortion. Water passages close to the seat remove heat and maintain the material within its design temperature. Cooling has no effect on compression ratio or clearance volume.

Question 6Marine Propulsion Systems and Main Engines

Which type of lubrication system supplies cylinder oil separately from the crankcase oil in a large two-stroke engine?

  1. Splash lubrication
  2. Oil mist lubrication
  3. Grease nipple lubrication
  4. Forced feed crankcase lubrication with separate cylinder lubricators Correct answer.

Explanation

Two-stroke crosshead engines use a total-loss cylinder lubrication system with mechanical lubricators feeding oil to the liner. The crankcase and running gear are lubricated by a separate forced circulation system, because the two oils have different properties.

Question 7Marine Propulsion Systems and Main Engines

What is the main reason for fitting a turbocharger to a marine diesel engine?

  1. To increase the mass of air trapped in the cylinder so that more fuel can be burnt Correct answer.
  2. To reduce the engine's mechanical noise
  3. To cool the lubricating oil
  4. To drive the camshaft

Explanation

A turbocharger uses exhaust gas energy to compress charge air, increasing its density. More air mass allows more fuel to be burnt per cycle, raising power output for a given swept volume. It does not drive the camshaft or cool the oil.

Question 8Marine Propulsion Systems and Main Engines

Which reading on the engine indicator diagram directly represents the work done per cycle?

  1. The slope of the expansion line
  2. The area enclosed by the pressure-volume curve Correct answer.
  3. The maximum cylinder pressure
  4. The height of the compression line

Explanation

On a pressure-volume diagram the enclosed area equals the net work output per cycle. Maximum pressure and the slopes of the lines are single-point or gradient values, not integrated work. Multiplying the area by the number of cycles per second gives indicated power.

Question 9Marine Propulsion Systems and Main Engines

A six-cylinder four-stroke engine runs at 600 rpm. What is the firing frequency in firings per minute?

  1. 300
  2. 600
  3. 1800
  4. 1200 Correct answer.

Explanation

A four-stroke cylinder fires once every two revolutions, so each cylinder fires at half the shaft speed. With six cylinders the total firing rate is 6 × 600 ÷ 2 = 1800 firings per minute. Confusing this with the shaft speed gives 600.

Question 10Marine Propulsion Systems and Main Engines

An engine develops 4000 kW brake power with a mechanical efficiency of 90 percent. What is the indicated power?

  1. 4444 kW Correct answer.
  2. 4800 kW
  3. 4000 kW
  4. 3600 kW

Explanation

Mechanical efficiency is brake power divided by indicated power. Rearranging gives indicated power = 4000 ÷ 0.90 = 4444 kW. The friction loss is the difference between indicated and brake power, about 444 kW.

Question 11Marine Propulsion Systems and Main Engines

During a scavenge fire in a large two-stroke engine, what is the first essential action after the fire is detected?

  1. Stop the cylinder lubricators
  2. Open the scavenge space inspection door to ventilate
  3. Reduce engine load and cut off fuel to the affected cylinder Correct answer.
  4. Increase the engine speed to blow out the fire

Explanation

A scavenge fire is starved of fuel and oxygen by reducing load and cutting fuel to the affected unit, then the scavenge space is sealed and the fixed firefighting system is applied. Opening an inspection door would admit air and endanger personnel. Cylinder lubrication must be maintained to protect the liner.

Question 12Marine Propulsion Systems and Main Engines

The exhaust gas temperature of one unit rises while its peak cylinder pressure falls. Which fault is most consistent with these readings?

  1. A worn turbocharger bearing
  2. A blocked fuel injector hole
  3. A high fuel oil viscosity
  4. A leaking exhaust valve Correct answer.

Explanation

A leaking exhaust valve allows hot gas to escape during compression and combustion, lowering peak pressure and raising exhaust temperature. A dribbling or blocked injector would normally raise peak pressure or cause uneven running. Turbocharger and fuel viscosity faults affect all units.

Question 13Marine Propulsion Systems and Main Engines

What is the function of the air cooler (charge air cooler) between the turbocharger and the scavenge air receiver?

  1. To preheat the fuel oil
  2. To remove water vapour from the exhaust gas
  3. To increase the pressure of the scavenge air
  4. To reduce the charge air temperature and thereby increase its density Correct answer.

Explanation

Compression in the turbocharger raises the air temperature, reducing its density. The air cooler removes this heat, so more air mass enters the cylinder and the thermal load on the engine is reduced. It does not change the pressure ratio appreciably.

Question 14Marine Propulsion Systems and Main Engines

Why is a crosshead guide fitted with white metal-lined slippers rather than running the crosshead directly on cast iron?

  1. To increase the compression ratio
  2. To provide a low-friction, replaceable bearing surface that can embed dirt Correct answer.
  3. To conduct electricity for the alarm system
  4. To reduce the weight of the crosshead

Explanation

White metal slippers provide a soft, conformable bearing surface that embeds abrasive particles and can be renewed when worn. Running steel directly on cast iron would cause rapid scoring and seizure. The slipper material does not affect compression ratio or weight significantly.

Question 15Marine Propulsion Systems and Main Engines

What is the purpose of the compression ring in a piston assembly?

  1. To scrape excess oil from the liner
  2. To support the weight of the piston
  3. To seal combustion gas and transfer heat from the piston to the liner Correct answer.
  4. To guide the piston rod

Explanation

Compression rings seat against the liner and groove to seal combustion gas and transfer heat from the piston crown to the cooled liner. Oil control rings scrape excess oil from the liner, and the piston rod is guided by the crosshead.

Question 16Marine Propulsion Systems and Main Engines

Which condition would cause the fuel injection pump rack to move towards the zero-fuel position on a governor-controlled engine?

  1. An increase in fuel oil temperature
  2. A decrease in scavenge air pressure
  3. A rise in engine speed above the set point Correct answer.
  4. A fall in engine speed below the set point

Explanation

The governor compares actual speed with the set point. If speed rises above the set point, the governor reduces fuel by moving the rack towards zero to restore speed. A fall in speed would increase fuel, and fuel temperature changes do not directly command the rack.

Question 17Marine Propulsion Systems and Main Engines

What is the main advantage of a common rail fuel injection system on a marine diesel engine?

  1. It removes the need for fuel filters
  2. It allows the engine to run without a governor
  3. It allows independent control of injection pressure and injection timing Correct answer.
  4. It eliminates the need for a fuel pump

Explanation

In a common rail system a high-pressure pump charges an accumulator, and electronic injectors control timing and duration. Injection pressure can therefore be set independently of engine speed and load, improving combustion and emissions. A pump is still required, and a governor is still needed.

Question 18Marine Propulsion Systems and Main Engines

A two-stroke engine has a scavenge air pressure of 1.8 bar absolute and a cylinder compression pressure of 60 bar gauge. What is the compression ratio's pressure rise, neglecting temperature effects?

  1. About 33 Correct answer.
  2. About 1.8
  3. About 60
  4. About 108

Explanation

The pressure rise from scavenge to compression is found by dividing the absolute compression pressure by the absolute scavenge pressure. Compression pressure is 61 bar absolute, so 61 ÷ 1.8 ≈ 34, close to 33. Temperature effects would reduce this figure slightly.

Question 19Marine Propulsion Systems and Main Engines

Why is a thrust block required between the engine crankshaft and the propeller shaft?

  1. To transmit the propeller thrust to the ship's hull Correct answer.
  2. To align the propeller shaft with the rudder
  3. To absorb torsional vibration
  4. To increase the engine speed

Explanation

The rotating propeller produces a thrust force along the shaft line. The thrust block contains tilting pad bearings that transmit this axial force to the hull structure, propelling the ship. It does not change speed or absorb torsional vibration.

Question 20Marine Propulsion Systems and Main Engines

A turbocharger suffers a sudden loss of speed and the engine exhaust gas temperature rises on all units. Which cause is most likely?

  1. Low cooling water temperature
  2. A broken fuel injection pipe
  3. A worn piston ring in one unit
  4. A fouled turbine nozzle ring Correct answer.

Explanation

A fouled turbine nozzle ring restricts gas flow, reducing turbocharger speed and scavenge air pressure. With less air available, combustion becomes incomplete and exhaust temperature rises on all units. A single-unit fault would not affect all cylinders equally.

Question 21Marine Propulsion Systems and Main Engines

What is the purpose of the indicator cock on a diesel engine cylinder head?

  1. To release trapped air before starting
  2. To connect an indicator or pressure gauge for measuring cylinder pressure Correct answer.
  3. To drain cooling water from the head
  4. To inject starting air into the cylinder

Explanation

The indicator cock provides access to the combustion chamber for fitting a mechanical or electronic indicator. This allows pressure-volume or pressure-time diagrams to be recorded for balancing and fault diagnosis. It is not a drain or starting air connection.

Question 22Marine Propulsion Systems and Main Engines

During a manoeuvring period, the engine must be reversed. What is the function of the reversing servomotor on a camshaft-operated engine?

  1. To change the direction of rotation of the crankshaft
  2. To reverse the direction of the scavenge air flow
  3. To shift the camshaft or cam followers so that the valve and fuel timing suit the new direction Correct answer.
  4. To reverse the cooling water pump

Explanation

The crankshaft rotation direction is set by the starting air and fuel timing. The reversing servomotor shifts the camshaft axially or swings the cam followers so that the correct cams act for the new direction. The scavenge air and cooling water flows are unaffected.

Question 23Marine Propulsion Systems and Main Engines

An engine shows a gradual fall in compression pressure across all units with normal exhaust temperatures. Which cause best explains this pattern?

  1. Incorrect fuel pump lead on one unit
  2. Worn piston rings and liners Correct answer.
  3. A blocked fuel injector on one unit
  4. A leaking exhaust valve on one unit

Explanation

A uniform fall in compression pressure on all units points to a common wear condition such as worn rings and liners or a general loss of scavenge air. Single-unit faults would produce unequal readings between units. Normal exhaust temperature indicates combustion is still acceptable.

Question 24Marine Propulsion Systems and Main Engines

Why is the exhaust gas boiler bypass arranged so that gas can be diverted around the boiler when the main engine is manoeuvring?

  1. To increase the turbocharger speed
  2. To reduce the engine's fuel consumption
  3. To increase the scavenge air pressure
  4. To prevent soot fires and corrosion when gas temperature is too low for the boiler Correct answer.

Explanation

At low load the exhaust gas temperature may fall below the acid dew point, causing corrosion, and unburnt products can deposit and ignite in the boiler. Bypassing the boiler during manoeuvring protects it from these conditions. The bypass does not affect turbocharger speed or fuel consumption.

Question 25Marine Propulsion Systems and Main Engines

A main engine governor is set to isochronous mode for a generator engine. What does isochronous control mean?

  1. Speed falls as load increases, giving a droop characteristic
  2. Fuel is held constant regardless of speed
  3. Speed is held constant at the set point regardless of load Correct answer.
  4. Speed is allowed to float freely with load

Explanation

Isochronous governing maintains a constant speed set point as load varies, which is required for a generator to hold frequency. Droop control deliberately allows speed to fall with load, and constant fuel would give no speed control at all.

Question 26Marine Propulsion Systems and Main Engines

In a four-stroke cycle marine diesel engine, during which stroke is the intake valve open and the exhaust valve closed?

  1. Power stroke
  2. Intake stroke Correct answer.
  3. Compression stroke
  4. Exhaust stroke

Explanation

The intake stroke draws fresh air into the cylinder, so the intake valve must be open and the exhaust valve closed. The other strokes involve different valve positions: compression and power have both valves closed, and exhaust has the exhaust valve open.

Question 27Marine Propulsion Systems and Main Engines

A marine diesel engine is running at 750 rpm and produces 1800 kW brake power. If the mechanical efficiency is 92%, what is the indicated power?

  1. 1800.0 kW
  2. 1656.0 kW
  3. 1956.5 kW Correct answer.
  4. 2070.0 kW

Explanation

Indicated power is brake power divided by mechanical efficiency. Here, 1800 kW / 0.92 = 1956.5 kW. This relationship shows that indicated power is always greater than brake power because friction losses are included.

Question 28Marine Propulsion Systems and Main Engines

Which component in a marine diesel engine directly converts the reciprocating motion of the piston into rotary motion of the crankshaft?

  1. Rocker arm
  2. Pushrod
  3. Camshaft
  4. Connecting rod Correct answer.

Explanation

The connecting rod links the piston to the crankshaft and, through its angular motion, converts the piston's linear reciprocation into crankshaft rotation. The camshaft, pushrods, and rocker arms are part of the valve train and do not perform this conversion.

Question 29Marine Propulsion Systems and Main Engines

A four-stroke auxiliary engine has a cylinder bore of 200 mm and a stroke of 300 mm. What is the mean piston speed at 900 rpm?

  1. 18.0 m/s
  2. 6.0 m/s
  3. 12.0 m/s
  4. 9.0 m/s Correct answer.

Explanation

Mean piston speed is calculated as 2 times the stroke times the rotational speed in revolutions per second. Stroke is 0.3 m and speed is 15 rev/s, so 2 × 0.3 × 15 = 9.0 m/s. This parameter is important for assessing piston and ring wear.

Question 30Marine Propulsion Systems and Main Engines

In a large two-stroke marine diesel engine, why is the exhaust valve typically opened before the piston reaches bottom dead centre?

  1. To allow the turbocharger to reach maximum speed before scavenging begins
  2. To ensure complete combustion of any remaining fuel
  3. To allow the cylinder pressure to fall to scavenge air pressure before the scavenge ports are uncovered Correct answer.
  4. To reduce the peak cylinder pressure during the power stroke

Explanation

Early opening of the exhaust valve allows the high-pressure combustion gases to blow down to a pressure near that of the scavenge air before the piston uncovers the scavenge ports. This prevents backflow of exhaust gas into the scavenge receiver and ensures efficient scavenging. It also reduces the work required to push out residual gases.

Question 31Marine Auxiliary Machinery and Systems

In a marine diesel engine cooling system, what is the primary function of the freshwater expansion tank?

  1. To act as a settling chamber for sludge from the cylinder jackets
  2. To increase the flow rate of the seawater cooling pump
  3. To chemically treat the cooling water with inhibitors
  4. To absorb thermal expansion of the coolant and maintain a static head on the pump suction Correct answer.

Explanation

The expansion tank allows the closed freshwater circuit to accommodate the volume change as the coolant heats and cools, and its elevated position provides a positive static head at the circulating pump suction to prevent cavitation. It is not a flow booster or a primary treatment vessel.

Question 32Marine Auxiliary Machinery and Systems

Which device is fitted in a marine fuel oil system to remove solid particles before the fuel reaches the high-pressure injection pump?

  1. A centrifuge separator
  2. A fuel booster pump
  3. A viscosity controller
  4. A duplex fuel filter Correct answer.

Explanation

Duplex filters are installed in the fuel supply line to trap solid particles, and the duplex arrangement allows one element to be cleaned while the other remains in service. Separators remove water and fine contaminants upstream but the final barrier before the injection equipment is the filter.

Question 33Marine Auxiliary Machinery and Systems

Why is a marine air compressor usually fitted with an intercooler between the low-pressure and high-pressure stages?

  1. To increase the discharge pressure of the final stage
  2. To reduce the compressed air temperature and improve volumetric efficiency of the next stage Correct answer.
  3. To lubricate the high-pressure piston
  4. To dry the air before it enters the air bottle

Explanation

Compressing air raises its temperature, and cooling it between stages reduces the work of compression in the following stage and improves volumetric efficiency. Lower interstage temperature also protects lubricants and materials from overheating.

Question 34Marine Auxiliary Machinery and Systems

What is the main purpose of a bilge separator on a ship?

  1. To store sludge for later incineration
  2. To supply seawater for firefighting
  3. To transfer bilge water directly overboard
  4. To separate oil from oily bilge water so that only water of acceptable oil content is discharged Correct answer.

Explanation

An oily water separator reduces the oil content of bilge water to the permitted discharge limit before the water is released overboard. The separated oil is retained for disposal ashore or incineration.

Question 35Marine Auxiliary Machinery and Systems

In a ship's steering gear, what is the function of the hunting gear?

  1. To lubricate the rudder stock bearings
  2. To return the pump control to the neutral position when the rudder reaches the ordered angle Correct answer.
  3. To limit the maximum rudder angle
  4. To provide emergency manual steering

Explanation

The hunting gear is a feedback linkage that moves the variable-delivery pump control back toward neutral as the rudder approaches the commanded angle, so the rudder stops at the ordered position. Without this feedback the pump would keep delivering oil and drive the rudder past the set point.

Question 36Marine Auxiliary Machinery and Systems

Which of the following is the normal method of producing fresh water on board a ship using waste engine heat?

  1. Electrodialysis
  2. Vacuum flash evaporation Correct answer.
  3. Reverse osmosis
  4. Freeze separation

Explanation

Vacuum flash evaporators use low-temperature waste heat from the main engine jacket water to evaporate seawater under vacuum, then condense the vapour into fresh water. The vacuum lowers the boiling point so that modest heat sources are sufficient.

Question 37Marine Auxiliary Machinery and Systems

What is the primary purpose of a purifier in a ship's fuel oil treatment system?

  1. To separate water and solid impurities from the fuel by centrifugal action Correct answer.
  2. To reduce the viscosity of the fuel before combustion
  3. To increase the calorific value of the fuel
  4. To measure the density of the fuel

Explanation

A purifier spins the fuel in a bowl so that denser water and solids move to the outer periphery while the cleaned oil flows toward the centre and is discharged. This centrifugal separation removes contaminants that would damage injection equipment.

Question 38Marine Auxiliary Machinery and Systems

A centrifugal pump is losing suction and the suction pressure gauge reads below atmospheric. Which condition most directly explains this behaviour?

  1. The suction strainer is partially blocked, causing a low net positive suction head Correct answer.
  2. The mechanical seal is leaking slightly
  3. The pump impeller is worn at the discharge edge
  4. The discharge valve is fully open and the pump is running at design speed

Explanation

A blocked suction strainer increases the pressure drop on the suction side, lowering the net positive suction head and causing cavitation or loss of suction. The low suction gauge reading is consistent with this restriction.

Question 39Marine Auxiliary Machinery and Systems

During routine operation, the pressure drop across a duplex fuel filter rises steadily and approaches the changeover limit. What is the correct immediate action?

  1. Change over to the standby filter element and clean the dirty one Correct answer.
  2. Open the filter bypass valve and continue running
  3. Reduce engine load to zero and stop the engine
  4. Increase the fuel temperature to maximum

Explanation

A rising differential pressure indicates the filter element is becoming blocked, so the standby element should be brought into service and the dirty element cleaned or renewed. Continuing on a heavily blocked element risks fuel starvation and injection equipment damage.

Question 40Marine Auxiliary Machinery and Systems

In a shell-and-tube lubricating oil cooler, the oil pressure is found to be lower than the seawater pressure. What is the main risk of this condition?

  1. Seawater will enter the oil system through any tube or joint leak, contaminating the oil Correct answer.
  2. The oil viscosity will increase excessively
  3. The oil pump will overspeed
  4. The cooler efficiency will rise above design

Explanation

The fluid at higher pressure leaks into the fluid at lower pressure. If seawater pressure exceeds oil pressure, any leak path allows seawater to contaminate the lubricating oil, which can cause corrosion and loss of lubrication.

Question 41Marine Auxiliary Machinery and Systems

A reciprocating bilge pump is found to deliver reduced capacity although the suction is clear and the pump speed is normal. Which fault is the most likely cause?

  1. An over-tightened packing gland
  2. A partially closed sea suction valve
  3. A higher than normal discharge head
  4. Worn or stuck suction and discharge valves Correct answer.

Explanation

Worn, broken, or stuck valves allow fluid to slip back past the valve seats during each stroke, reducing the volume actually displaced. With clear suction and normal speed, valve leakage is the most probable cause of lost capacity.

Question 42Marine Auxiliary Machinery and Systems

Why is the compressed air in a starting air bottle drained regularly?

  1. To remove condensed water that could corrode the bottle and cause valve malfunction Correct answer.
  2. To reduce the bottle pressure to a safe level
  3. To reduce the oxygen content of the air
  4. To increase the air temperature for easier starting

Explanation

Moisture condenses from compressed air inside the bottle, and accumulated water promotes internal corrosion and can be carried into starting valves, causing malfunction. Regular draining keeps the bottle and air system dry and reliable.

Question 43Marine Auxiliary Machinery and Systems

A ship's fresh water generator output falls while the engine load and jacket water temperature remain constant. Which cause is most likely?

  1. The vacuum in the evaporator has been lost completely
  2. The sea water feed temperature has decreased
  3. The evaporator shell has developed a scale layer on the heating surfaces Correct answer.
  4. The distillate pump has been stopped

Explanation

Scale on the heating surfaces adds thermal resistance, reducing heat transfer from the jacket water to the evaporating seawater and lowering the evaporation rate. With constant heat input and vacuum, fouling is the most likely cause of declining output.

Question 44Marine Auxiliary Machinery and Systems

In a two-stage air compressor, the intercooler and aftercooler drains are found to discharge very little water over a long period. Which conclusion is most reasonable?

  1. The compressor is running too slowly
  2. The moisture separators or drains may be blocked and should be checked Correct answer.
  3. The compressor is operating normally because compressed air is dry
  4. The air receiver is overpressurised

Explanation

Compressed air always carries some water vapour that condenses on cooling, so drains should regularly discharge condensate. Very little discharge over a long period suggests blocked drains or separators, which must be investigated to prevent water carry-over.

Question 45Marine Auxiliary Machinery and Systems

What is the purpose of the torque tube or torsion bar in a rotary vane steering gear?

  1. To transmit the rudder angle feedback to the hunting gear
  2. To lock the rudder in the midship position
  3. To provide a resilient connection that absorbs shock loads on the rudder Correct answer.
  4. To supply hydraulic oil to the vane chamber

Explanation

The torque tube or torsion bar provides a flexible link between the rudder stock and the control point, absorbing shock loads transmitted from the rudder and protecting the gear from damage. It also aids the feedback action of the control system.

Question 46Marine Auxiliary Machinery and Systems

A centrifuge purifier is producing clean oil with a high water content in the outlet. Which adjustment is most likely to correct the problem?

  1. Increase the fuel temperature beyond the recommended limit
  2. Reduce the bowl speed
  3. Increase the throughput rate through the purifier
  4. Reduce the throughput rate and adjust the interface position Correct answer.

Explanation

If the water interface is incorrectly positioned, water can be carried over with the cleaned oil. Reducing throughput increases residence time for separation, and adjusting the interface (for example by changing the gravity disc or back pressure) restores proper separation.

Question 47Marine Auxiliary Machinery and Systems

Why must the discharge valve of a positive displacement pump never be closed for long while the pump is running?

  1. Pressure will rise until the pump, piping, or relief valve is damaged Correct answer.
  2. The pump will lose its prime and stop
  3. The pump will reverse its direction of rotation
  4. The pump will overheat only because of friction in the bearings

Explanation

A positive displacement pump delivers a nearly fixed volume per revolution, so closing the discharge causes pressure to rise rapidly until something fails. A relief valve is fitted to protect the system, but the discharge must not be kept closed.

Question 48Marine Auxiliary Machinery and Systems

In a ship's sewage treatment plant using the biological (extended aeration) process, what happens if the plant is shut down for a long period without aeration?

  1. The bacteria remain fully active and the plant restarts immediately at full efficiency
  2. The chlorine dosing system becomes unnecessary
  3. The sludge volume decreases to zero
  4. The aerobic bacteria die off, and the plant needs time to re-establish the biomass before performance recovers Correct answer.

Explanation

Extended aeration relies on aerobic bacteria to break down organic matter. Without aeration the dissolved oxygen is depleted and the biomass dies back, so after a long shutdown the plant must be re-seeded and given time to rebuild the bacterial population before it treats sewage effectively.

Question 49Marine Auxiliary Machinery and Systems

A ship is required to comply with oil discharge limits from machinery space bilges. Which arrangement best ensures compliance during normal operation?

  1. Using a centrifugal purifier on the bilge water before discharge
  2. Discharging bilge water directly overboard when the ship is more than 12 nautical miles from land
  3. Passing bilge water through an oily water separator fitted with a 15 ppm oil content monitor and alarm Correct answer.
  4. Transferring bilge water to the fuel oil settling tank

Explanation

Machinery space bilge water must be processed through an oily water separator with an oil content monitor that alarms and stops discharge if the limit is exceeded, normally 15 ppm. This instrumentation provides continuous assurance that the discharge remains within the permitted limit.

Question 50Marine Auxiliary Machinery and Systems

A refrigeration plant using R404A is found to have a low suction pressure and a high discharge temperature with normal condenser cooling. What is the most likely cause?

  1. A condenser seawater valve fully open
  2. A correctly operating thermostatic expansion valve
  3. Undercharge of refrigerant or a restriction in the liquid line Correct answer.
  4. Overcharge of refrigerant

Explanation

A shortage of refrigerant or a restriction in the liquid line reduces the mass flow into the evaporator, lowering suction pressure, while the compressor works with less cooling and discharge temperature rises. Normal condenser cooling rules out condenser-side faults.